extraordinary Degree of Cold at Glafgow. 469 
down to the temperature of the air. The fheets of 
brown paper being fo thin acquired it fooneft, and when 
beheld in candle-light they became beautifully fpangled- 
over by innumerable reflections from the fmall cryftals 
of hoar-froft which had parted from the air. 
Evident fymptoms of the fame tendency of the air to 
depofit occurred on all the former nights of observing, 
by which the tubes of the thermometers were fo much 
ftained, that it required fome attention to keep that part 
which correfponded to the fcale quite clear. 
Thefe experiments indeed rather favour the opinion 
of the excefs of cold at prefent treated of depending 
upon a principle the very reverfe of evaporation. But 
till opportunities oiler in this or in a colder climate of 
making more experiments, it will be too early to fay 
any thing decifive concerning the nature or extent of a 
cooling process which has fo recently come under 
obfervation. All that can at prefent be affirmed is, that 
in certain circumftances fuch a procefs goes on, and that 
it depends probably upon principles different from eva- 
poration or chymical folution. At the fame time fome 
of the experiments flrew that a free communication be- 
twixt the hoar-froft and external air, perhaps whilft in 
motion, is neceffary; but in what manner this promotes 
the refrigeration doth not as yet appear. 
Q q q 2 
Thofe 
